Titanium-containing oxides, particularly as nanometer-sized particles, find utility in several technologies.
For example, nanophase titania (TiO2) particles have photocatalytic properties which may be beneficial in improving the efficiency of electrolytic decomposition of water into hydrogen and oxygen. Titania nanoparticles can also be used in dye-sensitized solar cells to produce electricity, and because they very efficiently absorb ultraviolet wavelengths while being virtually transparent to visible light, titania nanoparticles may be used to provide UV protection.
Among titanates, barium tetra-titanate (BaTi4O9) and alkaline metal hexa-titanate (M2Ti6O13; M=Na, K, Rb) are effective in promoting photolysis of water while lithium titanate (Li4Ti5O12) shows promise as an electrode material for the anode in lithium cells.
Titania is conventionally produced by oxidation of titanium chloride, for example by burning it in oxygen together with another combustible gas (often carbon monoxide). By adding seed crystals, the titanium dioxide is formed as a fine solid in a gas stream and is filtered out of the waste gases. Crystal growth is controlled by adding nucleating agents to the gas stream and the products are cooled by mixing with chlorine gas. The product is then washed and dried before milling and surface treatment. This process yields particles of conventional (micrometer) dimensions.
Nanosized titania particles may be fabricated by a number of different approaches, both liquid-based and vapor- or gas-based. The liquid-based processes include: sol-gel processes; hydrolysis processes; a hydrothermal process; a micro-emulsion process: the gas-based processes include; chemical vapor deposition; flame synthesis; vapor condensation; and laser ablation.
Although processes for direct manufacture of nanosized titania have been developed, most of the processes for fabrication of titanates call for co-sintering mixed oxides in appropriate proportion. The resulting titanate is therefore obtained in bulk form and must be milled, or otherwise comminuted, to reduce it to nano dimensions.
Thus there is need for reaction schemes and processing capable of producing at least nanosize titanium-containing oxide particles.